Ah, "not a word of boolean". I guess that's the opposite of not a bit of integer!
Anyway, I think the reason they don't mention Boolean specifically is that, as some other poster have referred to, the communications driver would probably never retrieve a single bit of data at any time. I've used some HMI/SCADA systems where if you configure a single Boolean tag, you actually find that a whole word (16x) is being retrieved. The other 15 bits are being ignored and only the value you require is loaded in to the tag. If you configure a second Boolean tag whose address lies within the span of those 15 bits, you don't increase your comms traffic at all. You still retrieve a word, but this time make use of 2 of the bits rather than 1. If you are fortunate (or plan well), you can configure 16 contiguous bits and your comms traffic is still only one word. This data packing is common and seems well understood. And I'd leave the PLC to get on with this part: making sure the right states end up assigned to the right bits.
What may influence how you achieve the rest is how the SCADA treats the 16 bits you send to it. Some may have strict data-typing, just like PLCs themselves. If you declare the data as an INT, it may be that the only instructions the SCADA permits on it are arithmetic functions. These are not much use for isolating individual bit states. However if the data is a WORD data type, these should include logical instructions such as ANDs ORs etc. Like the general opinions to date I wouldn't recommend ASCII or STRING data-types as the most effective for this.
Regards
Ken
